Method And Apparatus For Serving High Speed Downlink Shared Channel Cell Change

ABSTRACT

A method and apparatus for serving high speed downlink shared channel (HS-DSCH) cell change are disclosed. A wireless transmit/receive unit (WTRU) sends a measurement report to a radio network controller (RNC) when a signal strength of a target cell approaches a signal strength of a source cell. The RNC adds the target cell in an active set and sends pre-loaded HS-DSCH configuration information for the target cell to the WTRU. The WTRU sends another measurement report when a signal strength of the target cell exceeds that of the source cell. The WTRU monitors a high speed shared control channel (HS-SCCH) on the target cell based on the pre-loaded HS-DSCH configuration information and decodes an HS-SCCH transmission. The WTRU determines whether a MAC-hs/ehs reset is required and if so resets a MAC-hs/ehs entity prior to receiving an HS-DSCH transmission from the target cell.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/362,580, filed Jan. 30, 2009; which claims the benefit of U.S.Provisional Patent Application Nos. 61/025,625, filed Feb. 1, 2008 and61/087,413, filed Aug. 8, 2008, the contents of which are incorporatedby reference herein.

FIELD OF INVENTION

This application is related to wireless communications.

BACKGROUND

High speed downlink packet access (HSDPA) is a feature introduced inRelease 5 of the third generation partnership project (3GPP)specification. HSDPA achieves maximum spectral efficiency using threekey concepts: adaptive modulation and coding (AMC), fast physical layerretransmissions by implementing hybrid automatic repeat request (HARQ),and fast Node B scheduling.

Handover is a process in which a wireless transmit/receive unit (WTRU)switches from one cell to another without service interruption. When ahandover occurs, the WTRU needs to switch to a new serving HS-DSCH cell(target cell) and stop communicating with the old serving HS-DSCH cell(source cell). This procedure is also called serving HS-DSCH cellchange.

A WTRU continuously monitors signal strength of neighboring cells and aserving HS-DSCH cell. When a signal strength measured on a common pilotchannel (CPICH) of a neighboring cell exceeds that of the serving cell,(i.e., Event 1D), the WTRU sends a radio resource control (RRC)measurement report to a radio network controller (RNC) to report thechange of the best cell. The measurement report triggered by Event 1Dcontains the measured value and the cell identity (ID).

Upon reception of the event 1D measurement report, the RNC makes adecision to perform a handover to a target cell. A serving radio networkcontroller (SRNC) requests a controlling radio network controller (CRNC)to allocate HS-DSCH resources for the WTRU, (such as HS-DSCH radionetwork temporary identity (H-RNTI), high speed shared control channel(HS-SCCH) codes, HARQ resources, etc.), in the target cell via radionetwork subsystem application part (RNSAP) and Node B application part(NBAP) messages. Once the HS-DSCH resources are reserved the CRNCprovides all the information to the SRNC which in turn sends an RRCmessage to the WTRU. The RRC message that may be used to indicate aserving HS-DSCH cell change may include physical channelreconfiguration, transport channel reconfiguration, radio bearerreconfiguration, active set update, or the like. The RRC messageprovides the WTRU with the radio access parameters required for the WTRUto start monitoring the target cell. In addition, the RRC message mayprovide an activation time at which the handover should take place.

The handover may be either synchronized or unsynchronized. In anunsynchronized handover, the network and the WTRU do not activate theresources and switch at the same time. The activation time for the WTRUis set to “now”. This reduces the delays associated with the handoverprocedure. However, it increases the probability of data loss.

In a synchronized handover, the network and the WTRU perform the changeof resources simultaneously. However, the network has to set theactivation time conservatively to account for any kind of delays, suchas scheduling delay, retransmissions, configuration time, etc.Therefore, even though the synchronized handover minimizes data losses,it results in longer delays.

Conventionally, the RRC handover message is sent to the WTRU via thesource Node B. The delay associated with the serving HS-DSCH cell changemay cause the RRC handover message to fail, resulting in an unacceptablerate of dropped calls.

Several proposals have been made to optimize the serving HS-DSCH cellchange procedure. In accordance with the proposals, a WTRU and a Node Bmay be pre-loaded, (i.e., pre-configured), with the HS-DSCHconfiguration information, i.e. target cell pre-configuration.

Target cell pre-configuration adds robustness to the serving HS-DSCHcell change procedure by allowing the network to send the servingHS-DSCH cell change command either over the source cell and/or thetarget cell using the HS-SCCH. The target cell pre-configuration isprovided to the WTRU via an active set update procedure. Morespecifically, when a cell is added to the active set, (i.e., event 1A or1C is triggered), the network sends an active set update message to theWTRU, which, in addition to the dedicated physical channel information,includes the HS-DSCH serving cell information of the new cell, (such asthe H-RNTI, HS-DSCH, etc.).

When an event 1D is triggered and the WTRU transmits a measurementreport to request a serving cell change to the target cell, the WTRUstarts to monitor the HS-SCCH of the target cell (using the target cellpre-configured information) in addition to the HS-SCCH set in the sourcecell. The network may then send an HS-SCCH in the target cell to triggera serving cell change. Upon reception of the HS-SCCH on the target cellthe WTRU executes the HS-DSCH serving cell change to this target cell.

In the conventional serving HS-DSCH cell change procedure, the WTRUperforms a MAC-hs or MAC-ehs reset when an inter-Node B handover occurs,which is explicitly indicated to the WTRU from the network. The networksignals to the WTRU if a MAC-hs/ehs reset is required via a MAC-hs/ehsreset indicator in the handover message. If the MAC-hs/ehs indicator isset, the WTRU performs a MAC-hs/ehs reset. Otherwise, a MAC-hs/ehs resetis not performed. With the introduction of the new changes in accordancewith the above proposals, some problems may occur.

First, when Event 1D occurs (change of the best cell), the WTRU startsmonitoring an HS-SCCH in the target cell while still monitoring anHS-SCCH(s) in the source cell. If an HS-SCCH order is received from thetarget cell confirming change of serving cell the WTRU has no method ofdetermining whether a MAC-ehs or MAC-hs reset is required. This is dueto the fact that the target HS-SCCH does not contain an explicitindicator to order the WTRU to perform a reset, as is done with the RRChandover command. A reset will be required if the network performed aninter-Node B handover or an intra-Node B handover whereby the MAC-hs orMAC-ehs context is reset on the network side. The WTRU has no method ofdetermining that such a reset has been performed on the network side. AMAC-ehs or MAC-hs reset procedure comprises resetting the transmissionsequence number (TSN) values to zero, flushing the hybrid automaticrepeat request (HARQ) buffers, etc. If the WTRU does not perform a resetthe WTRU will not be synchronized with the network, thus resulting inpotential loss of data.

In addition, when a handover occurs the WTRU switches to the target cellto receive downlink data traffic. However, it is unclear what happenswith the uplink traffic and how the WTRU is assigned the uplinkresources of the target cell. According to the current 3GPP RRCspecification, the serving HS-DSCH cell and the serving E-DCH cell haveto be identical. Therefore, efficient methods to perform the handover inthe uplink must also be defined.

Lastly, the network is not aware whether the WTRU supports the fastoptimized handovers. Therefore, the network may start transmitting thehandover message over the target cell, but the WTRU cannot receive itsince the WTRU does not support such capability. This would cause theHS-DSCH cell change to fail and thus the WTRU would have to fall toCELL_FACH and initiate a cell reselection to the target cell.

SUMMARY

A method and apparatus for serving HS-DSCH cell change are disclosed. AWTRU sends a measurement report to an RNC when a signal strength of atarget cell approaches a signal strength of a source cell. The RNC addsthe target cell in an active set and sends pre-loaded HS-DSCHconfiguration information for the target cell to the WTRU. The WTRUsends another measurement report when a signal strength of the targetcell exceeds that of the source cell. The WTRU monitors an HS-SCCH onthe target cell based on the pre-loaded HS-DSCH configurationinformation and decodes an HS-SCCH transmission from the target cell.The WTRU makes a determination as to whether or not a MAC-hs/ehs entityneeds to be reset. The WTRU may reset the MAC-hs/ehs entity if aconfiguration parameter indicating to perform a MAC-hs/ehs reset isincluded in the pre-loaded HS-DSCH configuration information and is setto TRUE, or if the configuration parameter is not included or is not setto TRUE, but if transmit power control (TPC) combination indexes(optionally enhanced dedicated channel (E-DCH) relative grant channel(E-RGCH) combination indexes) of the source cell and the target cell aredifferent. The WTRU may reset the MAC-hs/ehs entity if it is detectedthat a Node B that controls the target cell and the source cell supportMAC-hs/ehs preservation. Alternatively, E-DCH configuration informationfor the target cell may be pre-loaded along with the pre-loaded HS-DSCHconfiguration information or may be provided in a handover command. TheHS-DSCH transmission including a handover command may be transmittedusing common HS-DSCH resources.

BRIEF DESCRIPTION OF THE DRAWINGS

A more detailed understanding may be had from the following description,given by way of example in conjunction with the accompanying drawingswherein:

FIG. 1 is a signaling diagram of an example process in accordance withone embodiment;

FIG. 2 is a flow diagram of an example process for performing aMAC-hs/ehs reset; and

FIG. 3 is a block diagram of an example WTRU.

DETAILED DESCRIPTION

When referred to hereafter, the terminology “WTRU” includes but is notlimited to a user equipment (UE), a mobile station, a fixed or mobilesubscriber unit, a pager, a cellular telephone, a personal digitalassistant (PDA), a computer, or any other type of user device capable ofoperating in a wireless environment. When referred to hereafter, theterminology “Node B” includes but is not limited to a base station, asite controller, an access point (AP), or any other type of interfacingdevice capable of operating in a wireless environment. Hereinafter, theterminology “MAC-hs/ehs” will be used to refer to either MAC-hs orMAC-ehs.

Where referred to hereafter decoding of HS-SCCH on the target cell, ortarget cell HS-SCCH refers to an HS-SCCH order sent by the target cellas an indication that the WTRU may perform an HS-DSCH serving cellchange to the target cell.

In accordance with one embodiment, in order to ensure that a WTRUsuccessfully receives data from a target cell after decoding an HS-SCCHand performs the serving cell change, the WTRU performs a MAC-hs/ehsreset prior to receiving data on an associated HS-PDSCH over the targetcell. FIG. 1 is a signaling diagram of an example process 100 inaccordance with one embodiment. A WTRU sends a measurement report to anRNC when a signal strength of a target cell approaches a signal strengthof a serving cell (step 102). The RNC determines to add the target cellto the active set and pre-loads the WTRU with the HS-DSCH configurationinformation for the target cell (step 104). The WTRU receives thepre-loaded HS-DSCH configuration information for the target cell andstores the pre-loaded HS-DSCH configuration information in a memory(step 106). The WTRU sends another measurement report (Event 1D report)when a signal strength of the target cell exceeds that of the sourcecell (step 108). The WTRU then monitors an HS-SCCH on the target cell inaddition to the HS-SCCH(s) on the source cell based on the pre-loadedHS-DSCH configuration information (step 110). The WTRU decodes theHS-SCCH (i.e., HS-SCCH order) on the target cell (step 112). The WTRUmakes a determination regarding whether or not to perform a MAC-hs/ehsreset (step 114). If the MAC-hs/ehs reset is required, the WTRU resets aMAC-hs/ehs entity prior to receiving an HS-DSCH transmission from thetarget cell (step 116). It is understood that the MAC-ehs/hs reset willbe performed at the time of the serving cell change. If an activationtime is specified the MAC-hs/ehs reset will be performed at the givenactivation time, when the serving cell change is performed and the WTRUreconfigures to the target cell.

The trigger of the MAC-hs/ehs reset may be the reception of the firstHS-SCCH from the target cell with an assigned H-RNTI. The WTRU may beassigned an H-RNTI for the target cell (a target H-RNTI) as part of thepreloaded HS-DSCH configuration information and may monitor two H-RNTIssimultaneously, (i.e., monitors an HS-SCCH on the target cell with thetarget H-RNTI and an HS-SCCH on the source cell with an H-RNTI for thesource cell (source H-RNTI)).

Alternatively, the WTRU may monitor an HS-SCCH on the target cell with asource H-RNTI. In this case, the network must ensure that no other WTRUin the target cell is assigned the same H-RNTI that is assigned to theWTRU in the source cell, (i.e., serving cell).

Alternatively, the WTRU may monitor a common H-RNTI. The common H-RNTImay be obtained from the broadcast control channel (BCCH) using asimilar method as in enhanced CELL FACH. The network may use the commonH-RNTI in the target cell to transmit the handover message to the WTRU.The network may assign a common H-RNTI to a group of WTRUs as part ofthe pre-loaded HS-DSCH configuration information. The WTRU may monitorthis common H-RNTI in the target cell and change it to a dedicatedH-RNTI upon reception of the handover command over the target cell.

The WTRU may perform a full MAC-hs/ehs reset upon decoding the targetcell HS-SCCH as if a MAC-hs/ehs reset indicator was set. Alternatively,the WTRU may perform a partial MAC-hs/ehs reset. In this case, the WTRUmay only reset the TSN and reinitialize reordering variables and timersof the MAC-hs/ehs queue to which a logical channel carrying a signalingradio bearer (SRB) is mapped. After decoding the HS-SCCH, the WTRUresets the TSN, variables, and timers of the queue configured with theSRB carrying the handover command. In case only one MAC-hs/ehs queue isreset, it is possible that the trigger for the partial MAC-hs/ehs resetis the transmission of an event 1D measurement report by the WTRUinstead of the detection of the HS-SCCH on the target cell. Afterreception of the handover command the WTRU may reset the wholeMAC-hs/ehs entity if the MAC-hs/ehs reset indicator is set.

In pre-Release 8 3GPP systems, if an intra-Node B handover occurs andthe Node B supports MAC-hs/ehs preservation, the WTRU does not need toperform a MAC-hs/ehs reset since both the source cell and the targetcell are controlled by the same Node B. MAC-hs/ehs preservation refersto a Node B or network that is capable of transferring or sharing theMAC-hs/ehs context and therefore does not have to reset any MAC-hs/ehsvariables and flush any buffers. If a serving cell change occurs withincells that support MAC-hs/ehs preservation, the WTRU is not required toperform a MAC-hs/ehs reset. However, if the WTRU bases the MAC-hs/ehsreset on the reception of the target cell HS-SCCH, the WTRU may alwaysreset the MAC-hs/ehs entity regardless of the type of handover eventhough it is not necessary. This may also result in a de-synchronizationbetween the WTRU and the network, if the Node B does not re-initializethe MAC-ehs/hs context, but the WTRU does.

The WTRU may use one or a combination of the following methods todetermine whether a MAC-hs/ehs reset is required when receiving thetarget cell HS-SCCH on the target cell. The WTRU may be assigned two ormore HS-SCCH codes to monitor in the target cell. The signal to performa MAC-hs/ehs reset may be based on the HS-SCCH code used to schedule thefirst transmission. For example, if the network uses the first code aMAC-hs/ehs reset is performed. Otherwise, a MAC-hs/ehs reset is notperformed. The network may configure the WTRU with this information orthe WTRU is preconfigured to know which code will be used to indicate aMAC reset.

Alternatively, the network may use the sub-frame numbers to indicate ifa MAC-hs/ehs reset is required. For example, if the WTRU detects thetarget cell HS-SCCH on an even numbered sub-frame the WTRU performs aMAC-hs/ehs reset, and if the WTRU detects the target cell HS-SCCH on anodd numbered sub-frame, the WTRU does not perform a MAC-hs/ehs reset.

Alternatively, an HS-SCCH order may be used to indicate the WTRU toperform a MAC-hs/ehs reset. An HS-SCCH order may be used to indicate aserving cell change and the need to perform a MAC-hs/ehs reset, andanother HS-SCCH order may be used to indicate just a serving cell changewithout a MAC-hs/ehs reset. Alternatively, a specific HS-SCCH order maybe used to order a MAC-hs/ehs reset.

Alternatively, the WTRU may use information from the radio links of thecells in the active set in determining whether a MAC-hs/ehs reset isrequired. The WTRU may optionally use enhanced dedicated channel (E-DCH)relative grant channel (E-RGCH) information. If an E-RGCH combinationindex of the target cell is equal to that of the current serving E-DCHcell, (i.e., the source cell), the source cell and the target cellbelong to the same Node B, (i.e., the cells belong to the serving E-DCHradio link set (RLS)), and a MAC-hs/ehs reset is not required, unlessotherwise indicated in the handover command. If the target cell does notbelong to the serving E-DCH RLS, the WTRU may perform a MAC-hs/ehsreset. Optionally, the WTRU may perform a MAC-hs/ehs reset of the queuewhich is configured for the logical channel carrying an SRB, (i.e.,partial MAC-hs/ehs reset). Alternatively, a TPC combination index may beused. If a TPC combination index of the target cell is the same as thatof the source cell, the cells belong to the same Node B and a MAC-hs/ehsreset may not be performed.

Alternatively and additionally, a new configuration parameter, (i.e., aninformation element (IE)), may be added to the list of pre-loadedHS-DSCH configuration information that is provided as part of the activeset update procedure. This new configuration parameter indicates whethera MAC-hs/ehs reset should be performed when a serving cell change isperformed to this cell.

For example, the new configuration parameter may be in the form of a“MAC-hs/ehs reset index”, with an integer value from (0 . . . 5). Forthe cells that belong to the same Node B and support MAC-hs/ehspreservation, the “MAC-hs/ehs reset index” is set to the same value, andthe radio links with the same MAC-hs/ehs reset index have the ability toperform MAC-hs/ehs preservation when a serving cell change occursbetween them. When a serving cell change is triggered and the MAC-hs/ehsreset indexes of the source and the target cells are the same, the WTRUdoes not perform a MAC-hs/ehs reset. If the MAC-hs/ehs reset indexes ofthe source and target cells are different, the WTRU performs aMAC-hs/ehs reset upon reception of an HS-SCCH order or upon decoding thefirst HS-SCCH with the pre-configured H-RNTI on the target cell.

Alternatively, a new configuration parameter may be provided to indicatewhether the radio links belonging to the same Node B support MAC-hs/ehspreservation. For example, a one bit indicator, (a new IE), may beincluded in an RRC message that pre-loads the required HS-DSCHconfiguration information. This new information element will be referredto as “serving cell MAC reset indicator.” The serving cell MAC resetindicator indicates whether the current Node B supports MAC-hs/ehspreservation, (i.e., whether a MAC-hs/ehs reset should be performed). Ifthe serving cell MAC reset indicator in the pre-loaded configurationinformation is set to TRUE, the WTRU performs a MAC-hs/ehs reset. If theserving cell MAC reset indicator is not set to TRUE, the WTRU combinesthis information with the radio link information of the E-RGCHcombination index or the TPC combination index. More specifically, theWTRU uses the TPC combination index (or optionally the E-RGCHcombination index) to determine if the MAC-ehs/hs reset should beperformed. If both the source cell and the target cell have the same TPCcombination index (or optionally the same E-RGCH combination index) theradio links belong to the same radio link set, (i.e., same Node B) andif the serving cell MAC reset indicator is not set to TRUE, the WTRUdetermines that the Node Bs support MAC-hs/ehs preservation and thus noMAC-hs/ehs reset is required. If the serving cell MAC reset indicatorindicates that the Node B supports MAC-hs/ehs preservation, (i.e., theserving cell MAC reset indicator is not set to TRUE), and if the sourcecell and the target cell have the same TPC combination index (optionallyE-RGCH combination index), the WTRU does not perform a MAC-hs/ehs reset.If the serving cell MAC reset indicator indicates that the Node B doesnot support MAC-hs/ehs preservation, (i.e., not set to TRUE), and if thesource cell and the target cell have different TPC combination indexes(optionally E-RGCH combination indexes), (i.e., belong to different NodeBs), the WTRU performs a MAC-hs/ehs reset upon reception of an HS-SCCHorder (indicating a serving cell change).

FIG. 2 is a flow diagram of a process for performing a MAC-hs/ehs resetin accordance with the embodiment disclosed above. A WTRU receives atarget cell HS-SCCH, (i.e., HS-SCCH order), (step 202). The HS-SCCHorder is passed to higher layers. It is determined whether the servingcell MAC reset indicator is set to TRUE (step 204). If the serving cellMAC reset indicator is set to TRUE, the WTRU performs a MAC-hs/ehs reset(step 206). If the serving cell MAC reset indicator is not set to TRUE,it is determined whether TPC combination indexes (optionally E-RGCHcombination indexes) of the source cell and the target cell aredifferent (step 208). If so, the WTRU performs a MAC-hs/ehs reset (step206). If not, the WTRU does not perform a MAC-hs/ehs reset.

In accordance with another embodiment, the WTRU does not perform a MACreset when reading an HS-SCCH on the target cell, but the networkensures that the data from the target cell is not discarded by using thenext TSN expected by the WTRU. This is performed by transferring theMAC-hs/ehs information from the source cell to the target cell. Thesource cell may only transfer the next TSN to be used for the queueconfigured with the SRB containing the handover command and possiblyother variables such as T1 timer values, etc. Alternatively, theinformation of all configured queues may be transferred to the targetcell. This will ensure that the WTRU does not discard the handovercommand

In accordance with another embodiment, the WTRU instantiates a newMAC-hs/ehs context, (i.e., TSN values for each reordering queues,reordering queues, etc.), as soon as the WTRU is provided with theH-RNTI to use in the target cell, while the MAC-hs/ehs context in thesource cell is still active. During a short period of time, the WTRUmaintains two MAC-hs/ehs contexts, one for the source cell and the otherfor the target cell. To facilitate hardware implementation, the physicalresources, (e.g., memory), may be shared between both contexts duringthat time. The WTRU may remove the MAC-hs/ehs context of the source celland allocate all physical resources to the MAC-hs/ehs context of thetarget cell when the WTRU is instructed to perform a MAC-hs/ehs reset byRRC signaling, or after the WTRU decodes its H-RNTI on the HS-SCCH onthe target cell.

In accordance with another embodiment, uplink E-DCH configurationinformation for the target cell is also pre-load simultaneously with theHS-DSCH configuration information. The E-DCH configuration informationmay include, but is not limited to, E-DCH absolute grant channel(E-AGCH) information, E-DCH radio network temporary identity (E-RNTI),transmission time interval (TTI), a serving grant value, reference E-DCHtransport format combination indexes (E-TFCIs), E-DCH HARQ indicatorchannel (E-HICH) information, and E-RGCH information. Other informationsuch as E-DCH dedicated physical control channel (E-DPCCH)-to-dedicatedphysical channel (DPCCH) power offset, E-DCH minimum set E-TFCI andother parameters may be provided simultaneously or be provided with thehandover command. It should be noted that if all required information isprovided as part of the pre-configured resources, the network may noteven need to send a handover command. More specifically, the WTRU mayperform a successful E-DCH and HS-DSCH serving cell change uponreception of an HS-SCCH order from the target cell, without the need tosuccessfully decode the RRC handover command.

Alternatively, the E-DCH configuration information for the target cellmay not be preloaded with the HS-DSCH configuration information, but maybe provided in the handover command sent to the WTRU over the targetcell. In order to carry on this procedure, the behavior of the WTRU hasto be modified. The WTRU may perform the following steps during thehandover procedure. When event 1D is triggered, the uplink transmissioncontinues normally with the source cell, (i.e., the serving E-DCH cell),while the target cell is in handover. At the time the WTRU decodes theHS-SCCH on the target cell, the WTRU immediately stops uplinktransmission in the source cell until the handover command is processedand the target cell is configured as a serving E-DCH cell.Alternatively, the WTRU continues transmitting data in the uplink to thesource cell even though the HS-SCCH is decoded in the downlink on thetarget cell. The WTRU switches to the target cell once the handovercommand is received and the E-DCH information is decoded. The change maytake place as soon as the configuration is completed, (i.e., theactivation time is set to “now”), or at the given activation time. Thiswould require that a serving E-DCH cell and a serving HS-DSCH cell arenot identical at all times. A slight delay may occur until the twobecome identical. Alternatively, a serving E-DCH cell and a servingHS-DSCH cell are not considered as changed until the handover command isreceived.

In accordance with another embodiment, the WTRU may trigger thetransmission of the scheduling information (SI) as soon as an HS-SCCH isdecoded on the target cell. This will allow the target cell to schedulethe WTRU appropriately. The SI may be sent as soon as the HS-SCCH isdecoded, or only after the successful reception of the first MAC PDUover the target cell. Alternatively, the SI may be sent as soon as theuplink is properly configured. The network may use the reception of theSI as an indication that the handover has been successful.

Additionally, the WTRU may also start fast channel quality indicator(CQI) reporting as soon as the first HS-SCCH is received. The frequencyof the CQI report may be more frequent than the configured CQI reportingfrequency. For example, the CQI may be sent X times on every Nconsecutive TTIs (where n≧1) and then it may fall back to normalbehavior. Alternatively, the CQI may be sent more frequently for a shortconfigured period of time or until the handover command is successfullyreceived. The network may schedule the first HS-SCCH with the assignedH-RNTI as a trigger for the WTRU to immediately start transmitting theCQI over the HS-DPCCH. Once the target Node B has received the first CQIor X CQI reports it may start data transmission in the downlink.

Alternatively, the WTRU may use the reception of the E-AGCH with itsE-RNTI over the target cell as an indication that the handover has takenplace on the network side, and thus switch to the target cell to monitorthe HS-SCCH on the target cell.

In accordance with another embodiment, new WTRU capability informationis added to an RRC message, (e.g., RRC connection request message), toindicate that the WTRU supports optimized HS-DSCH serving cell change.If the WTRU does not support it, the network does not pre-load theHS-DSCH or E-DCH configuration information and carry on the procedure.Alternatively, the WTRU implicitly knows not to perform the procedure ifthe pre-loaded HS-DSCH configuration information or E-DCH configurationinformation is not provided by the network. Alternatively, the optimizedHS-DSCH serving cell change procedure may be a mandatory feature for allWTRUs.

In accordance with another embodiment, the WTRU may use the commonHS-DSCH resources broadcasted on system information blocks (SIBs) orcommon resources provided to the WTRU as part of the active set updateprocedure to receive the HS-SCCH in the target cell. The commonresources provided to the WTRU via RRC signaling may be a common set ofresources that the WTRU may use for any scenarios where the serving cellchange occurs to a target cell for which the WTRU does not havepre-configured resources or the cell is not even in the WTRU's activeset. The network sends a handover command over the target cell or ahandover indication using the common resources either selected from theSIBs or the one assigned by the network to the WTRU. Only the WTRUswhich have reported an event 1D or event 1A or even 1C measurementreport are configured to listen to the common resource provided by thenetwork in the target cell. Due to the fact that a common resource isused, several WTRUs may be listening to the HS-SCCH code with the samecommon H-RNTI. Therefore, it is required to identify the destination ofthe RRC message. For the identification, a UTRAN radio network temporaryidentity (U-RNTI) of the WTRU may be added to the MAC header oralternatively to the RRC handover command. Alternatively, other WTRU IDssuch as H-RNTI, cell radio network temporary identity (C-RNTI), orE-RNTI may be appended to the MAC header.

Upon reception of the handover command over the target cell, if thecommand is for the WTRU, the WTRU reconfigures the downlink and uplinkresources according to the information provided in the handover message.This method would allow the network to allocate common resources to theWTRUs without wasting resources for all WTRUs that have the cell as partof the non-serving active set.

FIG. 3 is a block diagram of an example WTRU 300. The WTRU 300 includesa transceiver 302, a controller 304 and a memory 306. The WTRU 300 isconfigured to perform serving HS-DSCH cell change in accordance withembodiments disclosed above. The pre-loaded HS-DSCH configurationinformation and/or the pre-loaded E-DCH configuration information may bestored in the memory 306. The transceiver 302 is configured to monitoran HS-SCCH on the target cell based on the pre-loaded HS-DSCHconfiguration information and decode an HS-SCCH transmission from thetarget cell. The controller 304 is configured to control the transceiverto implement any embodiments disclosed above. For example, thecontroller 304 is configured to reset a MAC-hs/ehs entity prior toreceiving an HS-DSCH transmission from the target cell upon successfuldecoding of the HS-SCCH on the target cell if a configuration parameterindicating to perform a MAC-hs/ehs reset is included in the pre-loadedHS-DSCH configuration information and is set to TRUE, or if theconfiguration parameter is not included or is not set to TRUE, but ifTPC combination indexes of the source cell and the target cell aredifferent.

Although features and elements are described above in particularcombinations, each feature or element can be used alone without theother features and elements or in various combinations with or withoutother features and elements. The methods or flow charts provided hereinmay be implemented in a computer program, software, or firmwareincorporated in a computer-readable storage medium for execution by ageneral purpose computer or a processor. Examples of computer-readablestorage mediums include a read only memory (ROM), a random access memory(RAM), a register, cache memory, semiconductor memory devices, magneticmedia such as internal hard disks and removable disks, magneto-opticalmedia, and optical media such as CD-ROM disks, and digital versatiledisks (DVDs).

Suitable processors include, by way of example, a general purposeprocessor, a special purpose processor, a conventional processor, adigital signal processor (DSP), a plurality of microprocessors, one ormore microprocessors in association with a DSP core, a controller, amicrocontroller, Application Specific Integrated Circuits (ASICs), FieldProgrammable Gate Arrays (FPGAs) circuits, any other type of integratedcircuit (IC), and/or a state machine.

A processor in association with software may be used to implement aradio frequency transceiver for use in a wireless transmit receive unit(WTRU), user equipment (UE), terminal, base station, radio networkcontroller (RNC), or any host computer. The WTRU may be used inconjunction with modules, implemented in hardware and/or software, suchas a camera, a video camera module, a videophone, a speakerphone, avibration device, a speaker, a microphone, a television transceiver, ahands free headset, a keyboard, a Bluetooth® module, a frequencymodulated (FM) radio unit, a liquid crystal display (LCD) display unit,an organic light-emitting diode (OLED) display unit, a digital musicplayer, a media player, a video game player module, an Internet browser,and/or any wireless local area network (WLAN) or Ultra Wide Band (UWB)module.

What is claimed is:
 1. A method for serving high speed downlink sharedchannel (HS-DSCH) cell change, the method comprising: receiving anHS-SCCH order from a target cell indicating change of an HS-DSCH servingcell; determining a transmit power control (TPC) combination index of asource cell and a TPC combination index of the target cell; andresetting a MAC-hs/ehs entity on a condition that the TPC combinationindexes are different.
 2. The method of claim 1, further comprising:sending a first measurement report when a signal strength of the targetcell approaches a signal strength of the source cell; receiving targetcell HS-DSCH preconfiguration information; storing the target cellHS-DSCH preconfiguration information in a memory; sending a secondmeasurement report when a signal strength of the target cell exceedsthat of the source cell; and monitoring a high speed shared controlchannel (HS-SCCH) on the target cell based on the target cell HS-DSCHpreconfiguration information.
 3. The method of claim 2, wherein thetarget cell HS-DSCH preconfiguration information includes a serving cellMAC reset indicator, and the TPC combination index of the source celland the TPC combination index of the target cell are determined when theserving cell MAC reset indicator is not set to TRUE.
 4. The method ofclaim 2, wherein the target cell HS-DSCH preconfiguration informationincludes a serving cell MAC reset indicator, and the MAC-hs/ehs entityis reset when the serving cell MAC reset indicator is not set to TRUEand the TPC combination indexes are different.
 5. The method of claim 1,further comprising: determining enhanced dedicated channel (E-DCH)relative grant channel (E-RGCH) combination index of the target cell andthe E-RGCH combination index of the source cell; and resetting theMAC-hs/ehs entity on a condition that the E-RGCH combination indexes aredifferent.
 6. The method of claim 1, further comprising: receivingenhanced dedicated channel (E-DCH) preconfiguration information for thetarget cell along with target cell HS-DSCH preconfiguration informationand storing the E-DCH preconfiguration information in a memory; andperforming an E-DCH serving cell change using the E-DCH preconfigurationinformation when the HS-SCCH order is received in the target cell. 7.The method of claim 6, wherein the E-DCH preconfiguration informationincludes at least one of an E-DCH radio network temporary identity(E-RNTI), E-DCH absolute grant channel (E-AGCH) information, referenceE-DCH transport format combination indexes (E-TFCIs), E-DCH hybridautomatic repeat request (HARM) indicator channel (E-HICH) information,and E-DCH relative grant channel (E-RGCH) information.
 8. A wirelesstransmit/receive unit (WTRU) for serving high speed downlink sharedchannel (HS-DSCH) cell change, the WTRU comprising: a transceiverconfigured to receive a high speed shared control channel (HS-SCCH)order from a target cell indicating change of an HS-DSCH serving cell; acontroller configured to: determine transmit power control (TPC)combination index of a source cell and a TPC combination index of thetarget cell; and reset a MAC-hs/ehs entity on a condition that the TPCcombination index of the source cell and the TPC combination index ofthe target cell are different.
 9. The WTRU of claim 8, furthercomprising: a memory for storing target cell HS-DSCH preconfigurationinformation, wherein the controller is further configured to monitor aHS-SCCH on the target cell based on the target cell HS-DSCHpreconfiguration information and decode an HS-SCCH transmission from thetarget cell.
 10. The WTRU of claim 9, wherein the target cell HS-DSCHpreconfiguration information includes a serving cell MAC resetindicator, and the controller is configured to determine the TPCcombination index of the source cell and the TPC combination index ofthe target cell when the serving cell MAC reset indicator is not set toTRUE.
 11. The WTRU of claim 9, wherein the target cell HS-DSCHpreconfiguration information includes a serving cell MAC resetindicator, and the controller is configured to reset the MAC-hs/ehsentity when the serving cell MAC reset indicator is not set to TRUE andthe TPC combination indexes are different.
 12. The WTRU of claim 9,wherein the target cell HS-DSCH preconfiguration information includes aserving cell MAC reset indicator, and the controller is configured toreset the MAC-hs/ehs entity when the serving cell MAC reset indicator isset to TRUE.
 13. The WTRU of claim 8, wherein the controller isconfigured to determine an enhanced dedicated channel (E-DCH) relativegrant channel (E-RGCH) combination index of the source cell and anE-RGCH combination index of the target cell and reset the MAC-hs/ehsentity on a condition that the E-RGCH combination index of the targetcell and the E-RGCH combination index of the source cell are different.14. The WTRU of claim 8, wherein the controller is configured to resetthe MAC-hs/ehs entity on a condition that a Node B that controls thetarget cell and the source cell does not support MAC-hs/ehspreservation.
 15. The WTRU of claim 8, wherein the controller isconfigured to receive enhanced dedicated channel (E-DCH)preconfiguration information for the target cell along with target cellHS-DSCH preconfiguration information and perform E-DCH serving cellchange using the E-DCH preconfiguration information.
 16. The WTRU ofclaim 8 wherein the controller is configured to receive enhanceddedicated channel (E-DCH) configuration information for the target cellin a handover command and perform serving E-DCH cell change using theE-DCH configuration information.
 17. A method for serving high speeddownlink shared channel (HS-DSCH) cell change, the method comprising:sending a measurement report when a signal strength of a target cellexceeds a signal strength of a source cell; receiving a common HS-DSCHresource for the target cell; monitoring a high speed shared controlchannel (HS-SCCH) on the target cell using the common HS-DSCH resource;receiving an HS-SCCH order from the target cell indicating HS-DSCHserving cell change; and receiving a handover command message via thetarget cell.
 18. The method of claim 17 wherein the handover commandmessage includes an identity of a recipient of the handover commandmessage.
 19. A wireless transmit/receive unit (WTRU) configured toperform serving high speed downlink shared channel (HS-DSCH) cellchange, the WTRU comprising: a transceiver configured to monitor a highspeed shared control channel (HS-SCCH) on a target cell using a commonHS-DSCH resource for the target cell and receive an HS-SCCH orderindicating HS-DSCH serving cell change via the target cell; and acontroller configured to receive a handover command message via thetarget cell.
 20. The WTRU of claim 19 wherein the controller isconfigured to receive the handover command message based on an identityincluded in the handover command message.